Methods
From 1 July 2010 to 12 January 2011, all eligible participants in the Scottish Bowel Screening Programme, aged 50–74 years, resident in NHS Tayside and NHS Ayrshire & Arran, were sent a FIT kit pack containing a single sample collection device (Eiken Chemical Company, Tokyo, Japan).
The samples were analysed for f-Hb using OC-Sensor Diana automated immunoturbidimetric analysers (Eiken Chemical Company). Analyses were carried out by trained staff: the laboratory has a comprehensive total quality management system and is accredited to ISO15189-based standards by Clinical Pathology Accreditation (UK).
All participants with f-Hb≥400 ng Hb/ml buffer were reported as positive and referred for colonoscopy. This cut-off f-Hb was chosen to achieve approximately 2% positivity as per the current programme, selected for the available colonoscopy resource. Data for colonoscopy outcomes and any subsequent pathology were downloaded from clinical IT systems. Data on colonoscopy were collected on the quality of the investigation (quality of preparation, completeness of colonoscopy) and on the number, size and localisation of colorectal cancers and adenomas, and whether biopsy was performed. Full pathological data were collected on all excised/biopsy specimens including polyp type, presence or absence of malignancy, stage of any cancer and, in all adenoma, the severity of dysplasia. Lesion size was recorded from pathology reports except when removed piecemeal, when colonoscopy measurement was used. f-Hb was collated into clinical outcome groups according to most serious diagnosis. Assignment as HRA was ≥3 adenomas, or any adenoma with a maximum diameter ≥10 mm, taken from recommendation from the British Society of Gastroenterology as used in Scotland. f-Hb from those with adenoma were further grouped according to characteristics relating to their most serious lesion: size (small, a maximum dimension of <10 mm or large, ≥10 mm), degree of dysplasia (high or low-grade, HGD or low-grade dysplasia (LGD)), villous nature (presence or absence) and location (proximal defined as the region of the colon up to and including the splenic flexure, or distal, the region thereafter).
MedCalc (MedCalc Software, Mariakerke, Belgium) statistical software was used for all calculations. The Mann–Whitney U test was used for comparison between the groups and median lesion size. Probability of p<0.05 was considered significant.